When a batter has legs made out of jelly (normally an off-speed or curve ball heading at an unusual angle) and departs from a good batting stance. “His curve ball . . . it jelly-legs you.” - Phillies First Baseman Jim Thome, referring to Barry Zito's curve.[1]

To hit the ball hard, typically used to refer to pulling the ball over the fence for a home run. "Lee jerked one of his patented doubles into the left-field corner against Mets lefty Johan Santana."[2]

A player who is said to be juiced is thought to be taking performance-enhancing drugs. "It is now assumed, of course, that Bonds may well have been juiced on steroids at the time; the previous year he had set the all-time single-season record of 73 home runs, and his musculature was almost freakishly swollen."[3]

A baseball that is said to be juiced is doctored or manufactured in some way that makes it travel farther when a batter hits it. "Spectacular increases in home runs have often raised the question: Has the ball been juiced up to travel farther, in order to increase the number of home runs?"[4]

A fielder is said to get a good jump on the ball when he anticipates or reacts quickly to a batted ball and is thereby able to make a good play by fielding or catching it.[5] Also see crack of the bat.

A baserunner gets a good jump when he is able to leave the base well before the pitch reaches the plate. "Upsetting the timing of the baserunner can effectively prevent him from getting a good jump.... Base runners often read a pitcher's look and get their jump, or start, based on the pattern the pitcher establishes."[6]

breaking balls and knuckleballs, pitches that are difficult to hit due to movement rather than velocity. The term is also used to describe a "junk pitcher" or a junkball pitcher. "I couldn't believe he threw me a fastball because he had me down 1-2", Thames said. "He's usually a junk pitcher and he tried to sneak a fastball past me, and he left it up."[7] See also: Eephus pitch

A pitcher who throws predominantly junk, usually due to a weak (or slow) fastball. A junkballer or a junk artist: "Like all junk artists, Trujillo will have to prove himself at the higher levels before getting a shot at a major league job."[8] See also: Eephus pitch